The use of wiring boards containing strips of conductive metal tracking (typically made of copper) is common in electric circuit design, with electric-powered components mounted to the tracks provided on the board. Such tracks may be provided by the use of etching of copper onto a substrate material of the board.
It is also known to control high current through the use of multiple low-current-drawing electric-powered components connected in parallel with respect to each other and mounted to the tracks of such a wiring board, so as to achieve a higher power rating. Semiconductor devices are one example of such a low-current-drawing electric-powered component. However, there are problems with providing electric current to/from an arrangement of electric-powered components connected in parallel and mounted on such a wiring board. These problems may be understood from the discussion in the following paragraphs.
In a first example it is known to establish a common electrical connection with a wiring board to provide for current flow on/off the wiring board. It is known for the common electrical connection to be a location on a track of the wiring board from which multiple parallel paths subsequently branch off. Each branch provides for current flow to/from the electric-powered component(s) provided on the given branch. A problem arises due to the fact that the common electric connection on the wiring board is exposed to higher current flow than each of the individual parallel branches. This is due to the common electrical connection seeing the total amount of current which is subsequently shared between the various parallel branches. This relatively high current flow at the common electric connection on the wiring board requires the use of tracking of correspondingly larger cross-sectional area so as to manage the voltage drop on/off the wiring board and to avoid the tracking material melting. Maintaining a balanced impedance across an array of such electric-powered components mounted on a wiring board and connected in parallel with respect to each other to ensure that they each carry an equal load requires either: each individual conduction path of the different parallel paths being designed to enable this; or a grid of heavy grade conductive tracking being provided to connect the individual electric-powered components on the different parallel paths to the common electrical connection location located on the wiring board.
Both techniques (i) and (ii) above would require customisation of a conventional wiring board, with the disadvantages of increased complexity and weight (due to heavier conductive tracking being employed) in the design of the wiring board. Additionally, the heavier grade tracking necessary to carry the current flows on/off the wiring board is not readily suited to conveying lower level discrete analogue and digital signals to/from (often sensitive) electric-powered components mounted on the parallel branches of the wiring board tracking. To preserve signal integrity, where a grid of heavier grade tracking is employed to carry current flows on/off the wiring board, the board may have to also incorporate lighter grade tracking material to carry the lower level discrete analogue and digital signals. The use of different thicknesses of tracking on a wiring board has the disadvantage of increasing complexity of the wiring board's design and fabrication. Note that the terms “heavy” and “light” are used in a relative sense to refer to tracking of relatively larger and smaller cross-sections.
In a second example it is known for pinned connectors of a given fixed length to be used between a busbar and individual tracks on a wiring board, with the busbar spaced apart from the wiring board and acting as the common electric connection for current flow through different pinned connectors into respective tracks on the wiring board. Different ones of the pinned connectors establish separate parallel branches, of which the corresponding tracks to which each pinned connector joins form part. Significantly, the busbar and the wiring board are limited to being spaced a precise, fixed distance apart from each other to enable the pinned connectors to establish an electrical connection between the busbar and the wiring board. Although the use of such a configuration of pinned connectors ensures that no single part of the tracking on the wiring board is exposed to the total current flow entering or leaving the wiring board, the use of pinned connectors has a disadvantage of requiring each pinned connector to be separately fixed to the wiring board and/or the busbar (often by soldering)—a time-consuming task.
There is therefore a need to provide for an improved means of conveying current on/off a wiring board.
Accordingly, there is provided an electrical apparatus which includes a wiring board; at least one electrically conductive member spaced apart from and extending over at least part of the wiring board; at least first and second electric-powered components; and at least first and second resiliently-deformable electrically conductive connectors. The wiring board comprising at least first and second electrically conductive pathways, the first and second electric-powered components mounted to the first and second electrically conductive pathways respectively. The electrically conductive member and the wiring board arranged relative to each other such that the first and second resiliently-deformable connectors are compressed between the conductive member and the wiring board such that the first connector provides an electrical connection between the conductive member and the first electrically conductive pathway; and the second connector provides an electrical connection between the conductive member and the second electrically conductive pathway. The first and second resiliently-deformable connectors establish respective first and second parallel branches of an electric circuit from the conductive member, wherein the first branch comprises the first electrically conductive pathway and the first electric-powered component and the second branch comprises the second electrically conductive pathway and the second electric-powered component.
The wiring board may take any conventional form. Indeed, according to the present embodiments, the electrical apparatus allows high total current flows to be fed onto and/or off the wiring board without the need for significant customisation of the wiring board. The first and second electrically conductive pathways are conveniently provided to comprise tracks of electrically conductive material. Copper or another electrically conductive material may be used to form the tracks. The wiring board conveniently includes a fibrous substrate on or in which the tracks are mounted.
The electrically conductive member provides for electricity flow onto and/or off the wiring board. The conductive member is provided in any convenient form; for example, it may take the form of a bar, a rod or a plate made of copper, aluminium or another electrically conductive material known to the skilled person. Conveniently, the conductive member is provided as a busbar. The conductive member is conveniently provided such that it has a greater current carrying capacity than either of the first and second electrically conductive pathways of the wiring board; this thereby gives the conductive member the capacity to carry a total current flow in excess of that of the current carrying capacity of either of the first or second electrically conductive pathways and makes the conductive member suitable for providing the common electrical connection for current flow onto and/or off the wiring board.
The first and second resiliently-deformable electrically conductive connectors establish the respective first and second parallel branches of the electric circuit from the conductive member. Each resiliently-deformable electrically conductive connector carries a portion of the total current flow seen by the conductive member. The total current flow onto and/or off the wiring board is only seen by the conductive member. This configuration therefore avoids the need to upgrade the weight of tracking on a wiring board to enable any of the individual tracks to carry the total current flow on and/or off the wiring board.
The resilient-deformability of the connectors means that, when compared to use of known pinned connectors of a fixed length, it is possible to use a range of spatial separation distances between the electrically conductive member and the wiring board whilst still establishing electrical connection therebetween. The compressibility of the resiliently-deformable connectors also acts to promote retention of a reliable electrical connection of the connectors between the conductive member and the wiring board. In an embodiment, because the electrical connectors are resiliently-deformable, they permit the conduction of electricity between the conductive member and both of the first and second electrically conductive pathways without necessarily requiring the electrical connectors to be permanently fixed (for example, through the use of solder) to both the conductive member and the pathways. Rather, the electrical connectors can be retained in position solely as a consequence of compression of the electrical connectors between the wiring board and the respective first and second pathways of the wiring board. However, for assisting in ease of assembly, the connectors may be secured to the first and second electrically conductive pathways of the wiring board as this helps to ensure that a given connector establishes and maintains electrical connection with a given pathway. Solder or other known means may be used to secure the connectors to the conductive pathways.
Trials have been performed using metallic connectors in the form of spring contacts having a Z-shaped cross-sectional profile, with the connectors compressed between the electrically conductive member (provided in the form of a busbar) and corresponding tracks on the wiring board by virtue of opposing top and bottom end portions of the Z-shaped profile. Trials have also been performed using metallic connectors in the form of a spring contacts having a C-shaped cross-sectional profile. Steel, aluminium, brass or copper are other non-limiting examples of potentially suitable materials for the connectors, but other materials known to the skilled person may also be suitable subject to their having the necessary properties of being resiliently-deformable and electrically conductive.
The electric-powered components may take any form. However, the embodiments may be particularly beneficial when the electrical apparatus uses semiconductor devices as the components, with semiconductor devices generally understood to be low-power devices having low current requirements. The electrical connection in parallel of two or more such semiconductor devices in an electric circuit is able to provide benefits of a high power rating from the circuit.
In an embodiment, the at least one electrically conductive member comprises a first electrically conductive member and a second electrically conductive member, and the apparatus further includes a first set of the first and second resiliently-deformable electrically conductive connectors compressed between the first conductive member and the wiring board to thereby electrically connect in parallel the first conductive member to the first and second electric-powered components such that the first conductive member provides an input current along the first and second branches to the first and second electric-powered components respectively; and a second set of the first and second resiliently-deformable electrically conductive connectors compressed between the second conductive member and the wiring board to thereby electrically connect in parallel the second conductive member to the first and second electric-powered components such that the second conductive member receives an output current along the first and second branches from the first and second electric-powered components respectively.
The above-described arrangement allows the first set of the resiliently-deformable connectors to feed current from the first electrically conductive member onto the parallel-disposed first and second electrically conductive pathways of the wiring board to power the electric-powered components. The arrangement also allows the second set of the resiliently-deformable connectors to feed current off the wiring board from the electric-powered components through the parallel-disposed first and second electrically conductive pathways of the wiring board and onto the second electrically conductive member.
In an embodiment, the first and second electrically conductive members are arranged to face opposing outward-facing surfaces of the wiring board such that the wiring board is compressibly suspended between the first and second electrically conductive members by compression of the first and second sets of resiliently-deformable connectors, wherein the wiring board is configured such that the first electrically conductive pathway and the second electrically conductive pathway extend through the thickness of the wiring board. In this manner, the first and second sets of resiliently-deformable connectors help to isolate the wiring board and the components mounted thereon from mechanical shocks applied to either of the first or second conductive members. The degree of mitigation from mechanical shocks can be understood to be affected by the stiffness of the resiliently-deformable connectors.
Conveniently, the wiring board comprises vias extending between the opposing outward-facing surfaces of the wiring board so as to extend the first and second electrically conductive pathways through the thickness of the wiring board. This aspect may also be combined with electrically conductive tracks being provided on both of the opposed outward-facing surfaces of the wiring board, with each of the first and second electrically conductive pathways incorporating one or more tracks and vias. By way of non-limiting example, the first and second electric-powered components may be mounted to respective first and second groups of tracks provided on one of the opposed outward-facing surfaces of the wiring board, with vias establishing an electrically conductive pathway from these groups of tracks through the thickness of the wiring board to similar groups of tracks provided on the other outward-facing surface of the wiring board. The first and second sets of resiliently-deformable connectors may establish a direct physical connection to the first and second groups of tracks provided on the outward-facing surfaces of the wiring board, thereby enabling current flow from the first conductive member through the first set of resiliently-deformable connectors to the first and second groups of tracks (and the respective first and second electric-powered components mounted thereto), through corresponding vias to the corresponding groups of tracks on the other side of the wiring board, and then off the wiring board through the second set of resiliently-deformable electrical connectors to flow out into the second conductive member.
In an embodiment, a thermally conductive material is arranged between the at least one electrically conductive member and the wiring board. This aspect allows for improved conduction of heat away from the wiring board and out into the mass of the at least one conductive member. In an additional aspect, the thermally conductive material is arranged so as to conduct heat from one or both of the first and second electric-powered components to the conductive member. By way of non-limiting example, one or more pieces of thermally conductive foam may be arranged to directly contact the conductive member and one or both of the first and second electric-powered components. To enhance the ability to conduct heat generated by the electric-powered components away from the wiring board, either or both of the resiliently-deformable connectors and the conductive member may be formed of materials selected for their thermal conductivity. Use of a metallic material for the connectors may be beneficial because metals generally possess dual attributes of good thermal and electrical conductivity.
Conveniently, the at least one electrically conductive member is configured to provide electromagnetic shielding. For example and without limitation, the conductive member may be formed from aluminium or an alloy thereof, or other metallic materials.
In a further aspect, the apparatus further comprises a casing enclosing the wiring board, the at least one electrically conductive member forming at least a portion of the casing. To reduce or eliminate the risk of a person receiving electric shocks from current conveyed through the conductive member, in an embodiment, an outward-facing surface of the conductive member is provided with an electrically insulative coating thereon. Provision of an electrically insulative coating on an outward-facing surface of the conductive member would enable the conductive member to i) provide for current flow on and/or off the wiring board, and ii) at the same time, serve as all or part of an enclosure for the wiring board, where the exterior surface of enclosure is safe for a person to touch without fear of receiving an electric shock. For example, the electrically insulative coating may conveniently take the form of a plasticised or rubberised material.
Where the at least one electrically conductive member comprises first and second electrically conductive members arranged to face opposing outward-facing surfaces of the wiring board such that the wiring board is compressibly suspended between the first and second electrically conductive members (as described in the preceding paragraphs), the first and second conductive members may form at least a portion of the casing. This aspect provides enhanced physical protection for the wiring board due to being enclosed in whole or part by both of the first and second conductive members. To provide a person with protection from electric shocks, respective outward-facing surfaces of the first conductive member and the second conductive member may be provided with an electrically insulative coating thereon, as described above. Conveniently, a thermally conductive material is arranged between the wiring board and one or both of the first and second electrically conductive members, in a similar manner to that described above. This aspect provides for enhanced conduction of heat from heat generating components of the wiring board (such as the first and second electric-powered components). In an embodiment, the thermally conductive material is arranged so as to conduct heat from one or both of the first and second electric-powered components to one or both of the first and second conductive members.
Please note that the above figures are intended to illustrate non-limiting examples and are not drawn to scale.